An electromagnetic field sensor for measuring electromagnetic field of a micro region and an electromagnetic field measuring system using the sensor are well-known. FIG. 1A is a block diagram showing an example of a conventional electric field measuring system. FIG. 1B is a sectional view showing an electric field sensor used in the electric field measuring system. The electric field measuring system 820 includes, as shown in FIG. 1A, an optical fiber 801, a continuous laser beam source 800, a fiber amplifier 802, a polarization controller 803, an optical circulator 804, an electric field sensor 805, an analyzer 806, a fiber amplifier 807, a photo detector 808 and a spectrum analyzer 809. The electric field sensor 805 includes, as shown in FIG. 1B, the optical fiber 801, an electro-optic crystal 812 and a dielectric multilayer reflective layer 813. The electro-optic crystal 812 is a minute electric detecting element adhered to a front end of the optical fiber 801 via an adhesive layer 811. The dielectric multilayer reflective layer 813 is provided on a bottom surface of the electro-optic crystal 812 and reflects light.
Electric field detecting principles of the electric field measuring system 820 will be schematically described below. The continuous laser beam source 800 emits a laser beam. The fiber amplifier 802 amplifies the laser beam. The polarization controller 803 controls a polarization plane of the laser beam. The optical circulator 804 emits the laser beam to the electric field sensor 805. The dielectric multilayer reflective layer 813 provided on a bottom surface of the electro-optic crystal 812 reflects the laser beam. At this time, the refraction index of the electro-optic crystal 812 changes depending on an electric field generated from a circuit board 810. With such change, the polarization state of the laser beam propagating in the crystal is modulated based on an intensity of the external electric field. The optical circulator 804 returns the modulated and reflected laser beam to the optical fiber 801. The analyzer 806 converts the laser beam into intensity modulated light. The fiber amplifier 807 amplifies the converted laser beam. The photo detector 808 converts the amplified laser beam into an electric signal. The spectrum analyzer 809 detects the electric signal. A peak of the electric signal detected by the spectrum analyzer 809 corresponds to a signal caused by the external electric field. According to the principles of this system, signal intensity varies depending on the intensity of the external electric field. Thus, electric field distribution can be obtained by changing location of the electric field sensor 805 on the circuit board 810.
When the electro-optic crystal 812 in FIG. 1B is changed to a magneto-optic crystal, FIG. 1A shows a conventional magnetic field measuring system. Magnetic field detecting principles in this case are explained by changing electric field in the description of the above-mentioned electric field detecting principles to magnetic field.
The conventional electric field measuring system or the magnetic field measuring system employs an electric field sensor or a magnetic field sensor which is attached to the front end of the optical fiber. The electric field sensor or the magnetic field sensor has a configuration in which the electro-optic crystal 812 or the magneto-optic crystal produced by a micro-fabrication technique is adhered to the front end of the optical fiber. An applicable area and spatial resolution of the sensor are limited by a size of the crystal. That is, as the size of the crystal is smaller, the applicable area becomes smaller and the spatial resolution becomes higher. The spatial resolution is determined by the volume of the sensor beam propagating in the crystal. As the volume of the sensor beam is smaller, the spatial resolution becomes higher. For example, the conventional magnetic field sensor with the magneto-optic crystal adhered to a front end of the optical fiber can realize the spatial resolution of about 10 μm by using a crystal having 270 μm×270 μm in a plane size and 11 μm in thickness. With such configuration, however, further smaller sensor having higher spatial resolution cannot be realized due to limitation in a crystal micro-fabrication technique. In other words, a sensor applicable to a micro region of an LSI chip/package cannot be provided.
As described above, the conventional electromagnetic field sensor has the microfabricated crystal on the front end of the optical fiber. Generally, a plane size of a crystal is larger than a sectional area of a fiber. For this reason, it is difficult to tie a plurality of electromagnetic field sensors in a bundle. It is also difficult to prepare a plurality of crystals having the same thickness. Furthermore, it is difficult to prepare a plurality of sensors each having an adhesive layer of the same thickness which contributes to energy loss. For these reasons, it is impossible to constitute an electromagnetic field measuring system by tying a plurality of electromagnetic field sensors of the same spatial resolution and sensitivity. For these reasons, two-dimensional information cannot be measured without scanning sensors. The sensitivity of the magnetic field measuring system cannot be improved by signal processing between a plurality of sensors.
As techniques related to the above description, Japanese Laid-Open Patent Application JP-A-Heisei, 07-104013 discloses a probe. The probe includes glass blocks, a glass plate, a transparent electrode, electric-optic converting elements, dielectric multilayer reflective films, an electric wire, optical fibers, a fiber fixing part and a clamp part. The glass block has a front end part formed by cutting off a top of a pyramid-like quartz glass with a plane parallel to a bottom surface. The glass plate holds the plurality of the glass blocks in a line on the same plane. The transparent electrode is deposited simultaneously on a slant surface and a cut surface of each of the plurality of the aligned glass blocks. The electric-optic converting element is adhered to the front end of the glass block. The dielectric multilayer reflective film is placed on the electric-optic converting element and located on the surface opposite to the surface adhered to the glass block to reflect a laser beam. The electric wire is drawn from the transparent electrode. The optical fiber is located on the glass plate and guides the laser beam to the electric-optic converting element. The fiber fixing part fixes the optical fibers onto the glass plate. The clamp part clamps the fixing part and a surface of an object to be inspected which is opposite to an inspected surface.
Japanese Laid-Open Patent Application JP-A-Heisei, 06-82488 discloses a sensor for a light transformer. In the sensor for the light transformer, a Faraday element is disposed between a polarizer and an analyzer, and first and second fiber bundles composed of a plurality of optical fiber groups are provided on a light incidence side of the polarizer and on a light exit side of the analyzer, respectively. In the sensor for the light transformer, an end surface of the first fiber bundle directed toward a surface of the Faraday element is polished into a projecting spherical surface, and a dielectric film is formed on a surface of the polished portion so as to form the polarizer.
Japanese Laid-Open Patent Application JP-A-Heisei, 07-120504 discloses a voltage measuring apparatus. The voltage measuring apparatus has a laser beam source, an electro-optic member, reflecting means and detecting means. The laser beam source has first and second emitting end faces. The electro-optic member has a curved face with a high reflection coat formed on a surface thereof. A face opposite to the curved face is bonded to the first emitting end face of the laser beam source so that a center point of curvature of the curved face and a light emitting point on the first emitting end face of the laser beam source coincide with each other. The refraction index to the light varies depending on the electric field. The reflecting means is provided on the second emitting end face of the laser beam source. The detecting means detects a light intensity of the laser beam which penetrates through the reflecting means and emitted.
Japanese Laid-Open Patent Application JP-A-Showa, 59-145977 discloses a technique of a magnetic field measuring device. The magnetic field measuring device has a detecting part, an optical fiber and a measuring part. The detecting part attaches a polarizer and a Faraday rotary element on an end part or in the middle of the optical fiber. The optical fiber sends light to the detecting part and transfers the light from the detecting part. The measuring part connects the optical fiber to a light source and measures variation in the light from the detecting part.
Japanese Laid-Open Patent Application JP-A-Heisei, 11-67061 discloses a field emission cathode and a magnetic sensor. The field emission cathode is formed of a glass fiber cut to have a tapered surface at a front end thereof and carbon fibers embedded at a longitudinal center part of the glass fiber. A peripheral part of the glass fiber is coated with a conductive material with the glass fiber being electrically isolated from the carbon fibers.
Japanese Laid-Open Patent Application JP-P2001-281470A discloses a ferromagnetic material-containing optical fiber, a current sensor and a magnetic field sensor using the optical fiber. The current sensor has a light source for emitting light, a beam splitter for splitting incident light into two directions, a polarizing plate for linearly polarizing light, an optical fiber whose end face is covered with a magnetic film including particles of a ferromagnetic material, and a detector for detecting light. Light emitted from the light source enters the optical fiber through the beam splitter and the polarizing plate. The incident light reflects on an end opposite to an incident end of the optical fiber and is emitted from the incident end. The emitted light is incident to the detector through the polarizing plate and the beam splitter.
Japanese Laid-Open Patent Application JP-P2000-162566A discloses a magneto-optic effect enhancing element and a manufacturing method thereof. The magneto-optic effect enhancing element has a sandwiched structure in which a ferritic film is sandwiched between first and second dielectric multilayer reflective films so as to satisfy the Fabry-Perot resonance condition. The ferritic film is manufactured by a ferritic plating method at the range of 20° C. and 100° C.
Japanese Laid-Open Patent Application JP-A-Showa, 60-263866 discloses a technique of a photoelectric field sensor. The photoelectric field sensor has a Pockels element having a Pockels effect of generating a phase difference in orthogonal components of polarized light due to the electric field. The photoelectric field sensor has a sensor part including a polarizer, the Pockels element, a ⅛-wavelength plate and a reflecting mirror at the front end of the optical fiber. Through the optical fiber, light from a light source is transmitted to the Pockels element, passes through the Pockels element and is reflected on the reflecting mirror. The reflected light passes through the Pockels element again and is transmitted to a light-receiving part.
Another related technique is disclosed in T. Ohara, et al., “Two-Dimensional Field Mapping of Microstrip Lines with a Band Pass Filter or a Photonic Bandgap Structure by Fiber-Optic EO Spectrum Analysis System”, Proc. Int. Topical Meeting Microwave Photonics, Oxford, U. K., September 2000, pp. 210-213.
Another related technique is also disclosed in S. Wakana, et al., “Fiber-Edge Electro-optic/Magneto-optic Probe for Spectral-Domain Analysis of Electromagnetic Field”, IEEE Trans. Microwave Theory Tech., vol. 48, No. 12, December 2000, pp. 2611-2616.
Another related technique is also disclosed in E. Yamazaki, et al., “Three-Dimensional Magneto-optic Near-Field Mapping over 10-50 μm-Scale Line and Space Circuit Patterns”, Proc. the 14th Annual Meeting of the IEEE Lasers & Electro-optics Society, November 2001, p. 318.
Another related technique is also disclosed in E. Yamazaki, et al., “High-Frequency Magneto-Optic Probe Based on BiRIG Rotation Magnetization”, IEICE Trans. Electron., Vol. E86-C, No. 7, July 2003, pp. 1338-1344.
Another related technique is also disclosed in M. Iwanami, et al, “Wideband Magneto-optic Probe with 10 μm-Class spatial Resolution”, Japanese Journal of Applied Physics, Vol. 43, No. 4B, April 2004, pp. 2288-2292.